1. Field of the Invention
This invention relates to a lock, and more particularly to a two-handled lock that is operable to allow for or prevent co-rotation of a handle with a handle-connecting rod.
2. Description of the Related Art
Referring to FIGS. 1 and 2, an electric door lock disclosed in US Patent Application Publication No. 2007/0169525 includes an internal lock housing 11, an inside handle 12, an external lock housing 13, an outside handle 14, a handle-connecting rod 15 co-rotatable with the inside and outside handles 12, 14, two return units 16 for returning the inside and outside handles 12, 14, respectively, an electric driving unit 17, and a lock-controlling mechanism 2.
The external lock housing 13 includes a hole-defining wall 132 having a mounting hole 131 and two engaging grooves 134, and a projecting annular wall 133 disposed around the mounting hole 131. The outside handle 14 includes a handle housing 141, and a cylindrical part 142 disposed within and co-rotatable with the handle housing 141. The cylindrical part 142 is formed with two engaging holes 143 aligned respectively with the engaging grooves 134 in the external lock housing 13.
The lock-controlling mechanism 2 includes a rotary knob 21 mounted to the inside handle 12, a key-operated lockset 22 mounted to the outside handle 14, a lock-connecting rod 23 in the form of a plate and interconnecting the rotary knob 21 and the lockset 22, and two latching plates 24, 24′ sleeved on the lock-connecting rod 23 and aligned with the engaging grooves 134 in the external lock housing 13. Each of the latching plates 24, 24′ has a rod-engaging portion 242 having a rod-engaging hole 241, as well as a balance portion 243 and a retaining portion 244 extending from two opposite sides of the rod-engaging portion 242 and away from each other. The rod-engaging hole 241 in each of the latching plates 24, 24′ has a generally horizontal hole portion 245, and a generally vertical hole portion 246. The balance portion 243 of each of the latching plates 24, 24′ is aligned with the retaining portion 244 of the other of the latching plates 24, 24′ along a longitudinal direction of the lock-connecting rod 23.
When the latching plates 24, 24′ are disposed in latching positions shown in FIGS. 1 and 3, the lock-connecting rod 23 is vertical, and the retaining portions 244 of the latching plates 24, 24′ project respectively into the engaging grooves 134 in the external lock housing 13 to thereby prevent rotation of the inside and outside handles 12, 14. The lock can be locked through operation of any of the lockset 22, the rotary knob 21, and the electric driving unit 17 to move the latching plates 24, 24′ to the latching positions.
When the latching plates 24, 24′ are disposed in unlatching positions shown in FIG. 2, the lock-connecting rod 23 is horizontal, and the retaining portions 244 of latching plates 24, 24′ are retracted into the engaging holes 143 in the outside handle 14 to thereby allow for rotation of the inside and outside handles 12, 14.
Although the aforesaid door lock can achieve its intended purpose, the latching plates 24, 24′ are easily deformed and therefore malfunction when a large torque is applied thereto. This may be done by attaching a tool to the outside handle 14 to increase the moment arm associated with a torque applied to the outside handle 14. When the latching plates 24, 24′ are sufficiently deformed, the outside handle 14 can be pivoted to open the door.